In order to maintain healthy growth, plants must extract a variety of nutrients from the soil in which they grow. However, many soils are deficient in the necessary nutrients or the soils contain the nutrients only in forms which cannot be readily taken up by plants. To counteract these deficiencies, commercial fertilizing products containing select nutrients are commonly applied to soils in order to improve growth rates and yields obtained from crop plants. For example, phosphates may be added to soil to counteract a lack of available phosphorus.
In recent years, the use of plant growth-promoting rhizobacteria (PGPR) in fertilizers has increased. The PGPR colonize the roots of plants following inoculation into the rhizosphere and enhance plant growth. Rhizobacteria are also able to control plant diseases that are caused by other pathogenic bacteria and/or fungi. Disease is suppressed through induced systematic resistance and through the production of anti-fungal metabolites.
For optimum crop production, it is beneficial to use blends of different strains of rhizobacteria. Further, the fertilizer composition with which the PGPR is delivered must be optimized to sustain the PGPR during storage and during use. This is a particular challenge for liquid fertilizer compositions that have a relatively high water content.